Method and apparatus for scanning, stitching, and damping measurements of a double-sided metrology inspection tool

ABSTRACT

A system for inspecting specimens such as semiconductor wafers is provided. The system provides scanning of dual-sided specimens using a damping arrangement which filters unwanted acoustic and seismic vibration, including an optics arrangement which scans a first portion of the specimen and a translation or rotation arrangement for translating or rotating the specimen to a position where the optics arrangement can scan the remaining portion(s) of the specimen. The system further includes means for stitching the scans together, thereby providing both damping of the specimen and the need for smaller and less expensive optical elements.

This application is a continuation of U.S. patent application Ser. No.10/165,344, filed Jun. 7, 2002, now U.S. Pat. No. 6,686,996 entitled“Method and Apparatus for Scanning, Stitching, and Damping Measurementsof a Double Sided Metrology Inspection Tool,” inventors Paul J.Sullivan, et al., which is a continuation of co-pending U.S. patentapplication Ser. No. 09/335,673, filed Jun. 18, 1999, entitled “Methodand Apparatus for Scanning, Stitching, and Damping Measurements of aDouble Sided Metrology Inspection Tool,” inventors Paul J. Sullivan, etal., now U.S. Pat. No. 6,414,752, issued Jul. 2, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of optical imagingand more particularly to systems for sub-aperture data imaging of doublesided interferometric specimens, such as semiconductor wafers.

2. Description of the Related Art

The progress of the semiconductor industry over the last years hasresulted in a sharp increase in the diameters of semiconductor wafers asbase material for chip production for economic and process technicalreasons. Wafers having diameters of 200 and 300 millimeters arecurrently processed as a matter of course.

At present manufacturers and processors of wafers in the 200 and 300 mmrange do not have a wide range of measuring devices available whichenable inspection of particular geometric features, namely flatness,curvature, and thickness variation, with sufficient resolution andprecision.

As scanning of specimens has improved to the sub-aperture range, thetime required to perform full specimen inspection for a dual-sidedspecimen has also increased. Various inspection approaches have beenemployed, such as performing an inspection of one side of the specimen,inverting the specimen, and then inspecting the other side thereof. Sucha system requires mechanically handling the specimen, which isundesirable. Further, the act of inspecting the specimen has generallyrequired binding the specimen, which can cause deformation at the edgesof the specimen, increase defects at the edge, or cause bending of thespecimen during inspection.

One method for inspecting both sides of a dual sided specimen isdisclosed in PCT Application PCT/EP/03881 to Dieter Mueller andcurrently assigned to the KLA-Tencor Corporation, the assignee of thecurrent application. The system disclosed therein uses a phase shiftinginterferometric design which facilitates the simultaneous topographymeasurement of both sides of a specimen, such as a semiconductor wafer,as well as the thickness variation of the wafer. A simplified drawing ofthe Mueller grazing incidence interferometer design is illustrated inFIG. 1A. The system of FIG. 1A uses a collimated laser light source 101along with a lensing arrangement 102 to cause grazing of light energyoff the surface of both sides of the specimen 103 simultaneously. Asecond lensing arrangement 104 then provides focusing of the resultantlight energy and a detector 105 provides for detection of the lightenergy.

The design of FIG. 1A is highly useful in performing topographicalmeasurements for both sides of a dual-sided specimen in a singlemeasurement cycle, but suffers from particular drawbacks. First, thesystem requires minimum specimen movement during measurement, which canbe difficult due to vibration in the surrounding area and vibration ofthe specimen itself. Further, the inspection can be time consuming andrequires highly precise light energy application and lensing, which isexpensive. The specimen must be free standing and free of edge forces,and the incidence geometry during inspection must be unimpeded. Accessmust be preserved under all incidence angles. These factors providemechanical challenges for successfully supporting the specimen;excessive application of force at a minimum number of points may deformthe specimen, while numerous contact points impede access and requireexact position to avoid specimen deformation or bending duringinspection. Further, edge support of the specimen has a tendency tocause the specimen to act like a membrane and induce vibration due toslight acoustic or seismic disturbances. This membrane tendency combinedwith the other problems noted above have generally been addressed byincluding most components of the system within an enclosure thatminimizes ambient vibrations, which adds significant cost to the systemand does not fully solve all vibration problems.

The cost of lenses sized to accommodate inspection of a full wafer inthe arrangement shown in FIG. 1A are highly expensive, and generallyhave the same diameter as the diameter of the specimen, generally 200 or300 millimeters depending on the application. Full aperturedecollimating optics, including precision lenses, gratings, andbeamsplitters used in a configuration for performing full inspection ofa 300 millimeter specimen are extremely expensive, generally costingorders of magnitude more than optical components half the diameter ofthe wafer.

It is therefore an object of the current invention to provide a systemfor performing a single measurement cycle inspection of a dual-sidedspecimen having dimensions up to and greater than 300 millimeters.

It is a further object of the present invention to provide a system forinspection of dual-sided specimens without requiring an excessive numberof binding points and simultaneously allowing free access for inspectionof both sides of the specimen.

It is a further object of the current invention to provide for thesingle measurement cycle inspection of a dual-sided specimen whileminimizing the tendency for the specimen to behave as a membrane andminimize any acoustic and/or seismic vibrations associated with theinspection apparatus and process.

It is still a further object of the present invention to accomplish allof the aforesaid objectives at a relatively low cost, particularly inconnection with the collimating and decollimating optics and anyenclosures required to minimize acoustic and seismic vibrations.

SUMMARY OF THE INVENTION

The present invention is a system for inspecting a wafer, includinginspecting both sides of a dual sided wafer or specimen. The wafer ismounted using a fixed three point mounting arrangement which holds thewafer at a relatively fixed position while simultaneously minimizingbending and stress. Light energy is transmitted through a lensingarrangement employing lenses having diameter smaller than the specimen,such as half the size of the specimen, arranged to cause light energy tostrike the surface of the wafer and subsequently pass through secondcollimating lens where detection and observation is performed.

The system further includes at least one damping bar, where the numberof damping bars depends on the wafer repositioning arrangement. Theeffect of the damping bar is to perform viscous film damping, or VFD, ofthe non-measured surface of the specimen to minimize the effects ofvibration in accordance with VFD, or the Bernoulli principle. Eachdamping bar is positioned to be within close proximity of the surface tobe damped. The proximity between any damping bar and the surface of thewafer is preferably less than 0.5 millimeters, and spacing of 0.25 and0.33 may be successfully employed. Smaller gaps provide problems whenwarped specimens are inspected. One embodiment of the current inventionemploys a damping bar to cover slightly less than half of the specimenwhen in scanning position.

Mounting for the wafer uses a three point kinematic mount. The mountingpoints include clips having spherical or semi-spherical tangentiallymounted contacts, mounted to a support plate and arranged to besubstantially coplanar, where the clips are adjustable to provide forslight irregularities in the shape of the wafer. The adjustability ofthe contact points provide the ability to hold the wafer without a stiffor hard connection, which could cause bending or deformation, as well aswithout a loose or insecure connection, which could cause inaccuratemeasurements.

Light energy is conducted through a beam waveguide and then strikes adeviation mirror, is redirected onto a parabolic collimation mirror bytwo further deviation mirrors. The deviation mirrors are oriented at anangle of 90° relative to each other. The parallel light beam P reflectedfrom the parabolic mirror reaches a beam splitter through the twodeviation mirrors.

The beam splitter is formed as a first diffraction grating and isarranged in the apparatus in a vertical direction. The parallel lightbeam P strikes the diffraction grating in a perpendicular direction. Abeam collector in the form of a second diffraction grating is disposedfrom the first diffraction grating and parallel thereto. Behind the beamcollector two decollimation lenses are arranged at equal level. Thelight beams leaving the decollimation lenses are each deflected andfocused onto two CCD cameras through various deviation mirror pairs andto an optical imaging system.

The beam splitter is supported transversely to the optical axis andincludes a piezoelectric actuating element for shifting the phase of theparallel light beam P by displacing the diffraction grating.

A wafer or specimen to be measured is held on a holding device such thatboth plane surfaces are arranged in vertical direction parallel to thelight beam P. The wafer is supported substantially at its vertical edgeso that both surfaces are not substantially contacted by the supportpost and are freely accessible to the interferometric measurement.

A receiving device may be provided. Further, a reference apparatus maybe provided which comprises a reference body having at least one planesurface. The reference body can be introduced into the light pathbetween the first diffraction grating and the second diffraction gratingin place of the semiconductor wafer or specimen to be measured by meansof a traveller with a linear guide. The reference body is held so thatits plane surface is arranged in vertical direction parallel to theundiffracted light beam P.

Modifications of the imaging apparatus and method are possible. A bodyhaving two precisely plane parallel surfaces may be used for thereference body, whereby both surfaces are measured simultaneously.However, the embodiment having a single plane surface of the referencebody is more suitable.

In one arrangement, a light source initially emits light energy andstrikes two mirror surfaces, which each direct light energy through afirst collimating lens and simultaneously strike the two surfaces of thespecimen. Light energy is thereupon directed through a second pair ofcollimating lens and to a second pair of mirrors, toward a focusingelement arrangement, and a detector. A translation surface or mountingsurface holding the contact points and wafer or specimen is fastened toa translation stage, which provides translation or sliding of thespecimen within and into the lensing/imaging arrangement. The systemfirst performs an inspection of one portion of the specimen, and thetranslation stage and wafer are repositioned or translated such as bydriving the translating stage so that another portion of the wafer iswithin the imaging path. The other portion of the wafer is then imaged,and both two sided images of the wafer are “stitched” together.

Other means for presenting the remaining portion of wafer or specimenmay be employed, such as rotating the wafer mechanically or manually, orkeeping the wafer fixed and moving the optics and imaging components.Alternately, scanning may be performed using multiple two-sidedinspections of the module, such as three, four, or five or more scans ofapproximate thirds, quarters, or fifths, and so forth of the specimen.While multiple scans require additional time and thus suffer fromincreased throughput, such an implementation could provide for use ofsmaller optics, thereby saving overall system costs.

In a two phase scan of a dual sided specimen, at least 50 percent of thesurface must be scanned in each phase of the scan. It is actuallypreferred to scan more than 50 percent, such as 55 percent, in each scanto provide for a comparison between scans and the ability to “stitch”the two scans together.

Scanning and stitching involves determining the piston and tilt of thespecimen during each scan, adjusting each scan for the piston and tiltof said scan, and possibly performing an additional stitching procedure.Additional stitching procedures include, but are not limited to, curvefitting the points between the overlapping portions of the two scansusing a curve fitting process, replacing overlapping pixels with theaverage of both data sets, or weighting the averaging in the overlappingregion to remove edge transitions by using a trapezoidal function, halfcosine function, or other similar mathematical function. Backgroundreferences are preferably subtracted to improve the stitching result. Ifsignificant matching between the scans is unnecessary, such as in thecase of investigating for relatively large defects, simply correctingfor tilt and piston may provide an acceptable result. However, in mostcircumstances, some type of curve fitting or scan matching is preferred,if not entirely necessary.

These and other objects and advantages of the present invention willbecome apparent to those skilled in the art from the following detaileddescription of the invention and the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates the general concept of the predecessor Muellersystem for inspecting both sides of a semiconductor wafer or specimenwhen said specimen is oriented in a substantially “vertical”orientation;

FIG. 1B illustrates a first embodiment of the present invention,including the damping bar and dual sided lensing arrangement;

FIG. 2 presents the mounting points of the wafer or specimen;

FIG. 3 illustrates a measurement module for use in connection withtranslating the wafer and performing multiple scans in the presence ofmultiple damping bars;

FIG. 4A shows the first position of the wafer or specimen relative to adamping bar when a rotational scanning and stitching procedure isperformed on approximately half the wafer surface;

FIG. 4B is the second position of the wafer or specimen relative to adamping bar when a rotational scanning and stitching procedure isperformed on the other approximately half of the wafer surface;

FIG. 5A shows the first position of the wafer or specimen relative to adamping bar arrangement when a translational scanning and stitchingprocedure is performed on approximately half the wafer surface;

FIG. 5B is the second position of the wafer or specimen relative to adamping bar arrangement when a translational scanning and stitchingprocedure is performed on the other approximately half of the wafersurface;

FIG. 6 represents an algorithm for performing the scanning and stitchingaccording to the present invention;

FIG. 7 presents a conceptual schematic representation of the componentsand optics necessary to perform dual sided imaging of a semiconductorwafer; and

FIG. 8 is a top view of the components and optics which shows the pathof light energy.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1B illustrates a first embodiment of the present invention,specifically one for scanning both sides of a dual-sided wafer orspecimen 111. According to FIG. 1B, the wafer 111 is mounted using afixed three point mounting arrangement which is shown in FIG. 2. Thethree point mounting arrangement serves to hold the wafer 111 at arelatively fixed position while simultaneously minimizing any bending orstressing of the dual-sided wafer. Light energy is transmitted throughfirst collimating lens 112 which is arranged to cause light energy tostrike the surface of the wafer 111 and subsequently pass through secondcollimating lens 113 where detection and observation is performed. Asmay be appreciated by examining FIG. 1B, the diameter of both firstcollimating lens 112 and second collimating lens 113 are significantlysmaller than the diameter of the specimen or wafer 111, and incidentlight strikes only a portion of the surface of wafer 111. Not shown inthe illustration of FIG. 1B is that while light energy is striking thesurface of wafer 111 visible in the arrangement shown, light energysimultaneously passes through first collimating lens 112 and strikes thereverse side of the wafer 111, not shown in FIG. 1B. Light energy passesfrom the reverse side of the specimen 111 through second collimatinglens 113.

The arrangement further includes an upper damping bar 114 and a lowerdamping bar 115. In the arrangement shown in FIG. 1B, the upper dampingbar 114 covers approximately one half of the specimen 111, specificallythe half not being inspected. The effect of the damping bar is to dampthe non-measured surface of the specimen 111 to minimize the effects ofvibration. Damping in this arrangement is based on VFD, or the Bernoulliprinciple, wherein the upper damping bar 114 in the arrangement shown isbrought to within close proximity of the surface to be damped. Theproximity between either damping bar 114 or 115 and the surface of thewafer is preferably less than 0.5 millimeters, and spacing of 0.25 and0.33 may be successfully employed. The problem associated with providingsmaller gaps between either damping bar 114 or 115 and the surface ofwafer 111 is that any warping of the wafer may cause the bar to contactthe surface. For this reason, and depending on the wafer surface, gapsless than 0.10 millimeters are generally undesirable. Further, gapsgreater than 1.0 millimeters do not produce a desirable damping effect,as the Bernoulli principle does not result in sufficient damping in thepresence of gaps in excess of 1.0 millimeter.

The gap between the specimen 111 and upper damping bar 114 or lowerdamping bar 115 restricts airflow between the specimen and the dampingbar and damps vibration induced in the specimen. Each damping bar isgenerally constructed of a stiff and heavy material, such as a solidsteel member. Overall dimensions are important but not critical in thatthe damping bar should cover a not insignificant portion of the wafer111. Coverage of less than 20 percent of the wafer tends to minimize theoverall damping effect on the wafer, but does provide some level ofdamping.

The illumination of only a portion of the wafer 111 provides for usingsmaller lenses than previously performed. In the embodiment shown inFIG. 1B, the preferred size of the first collimating lens 112 and secondcollimating lens 113 is approximately 4.4 inches where the wafer 111 is300 millimeters in diameter. In such an arrangement, the damping bars114 and 115 are approximately 4.5 inches wide. Length of the dampingbars depends on the mode of wafer movement, as discussed below.

As shown in FIG. 2, the mounting for the wafer 111 is preferably using athree point kinematic mount, where the three points 201, 202, and 203represent spherical or semispherical contacts tangential to one another.Points 201, 202, and 203 are small clips having spherical orsemispherical tangentially mounted contacts, mounted to a support platesuch as mounting plate 116 to be substantially coplanar, with adjustableclips to provide for slight irregularities in the shape of the wafer111. The spherical or semispherical components should be sufficientlyrigid but not excessively so, and a preferred material for thesecomponents is ruby. The adjustability of points 201, 202, and 203provide an ability to hold the wafer 111 without a stiff or hardconnection, which could cause bending or deformation, as well as withouta loose or insecure connection, which could cause inaccuratemeasurements. In FIG. 1B, two lower kinematic mount points 202 and 203(not shown) support the lower portion of the wafer 111, while the upperportion is supported by mount point and clip 201. The points 201, 202and 203 are therefore stiff enough to mount the wafer or specimen 111and prevent “rattling” but not so stiff as to distort the wafer. Thespherical or semispherical contact points are generally known to thoseof skill in the mechanical arts, particularly those familiar withmounting and retaining semiconductor wafers. The combination of clampingin this manner with the Bernoulli damping performed by the damping bars114 and 115 serves to minimize acoustic and seismic vibration.

Simultaneous imaging of both sides of the specimen is performed inaccordance with PCT Application PCT/EP/03881 to Dieter Mueller,currently assigned to the KLA-Tencor Corporation, the assignee of thecurrent application. The entirety of PCT/EP/03881 is incorporated hereinby reference. This imaging arrangement is illustrated in FIGS. 7 and 8.As shown in FIGS. 7 and 8, the light energy directing apparatus employedin the current invention comprises a light source in the form of a laser801. The light emitted from the laser 801 is conducted through a beamwaveguide 802. The light produced by the laser 801 emerges at an end 803of the beam waveguides 802 so that the end 803 acts as a punctual lightsource. The emerging light strikes a deviation mirror 804 wherefrom itis redirected onto a collimation mirror 807 in the form of a parabolicmirror by two further deviation mirrors 805 and 806. Deviation mirrors805 and 806 are oriented at an angle of 90° relative to each other. Theparallel light beam P reflected from the parabolic mirror 807 reaches abeam splitter 808 through the two deviation mirrors 805 and 806.

The beam splitter 808 is formed as a first diffraction grating and ispreferably a phase grid. The beam splitter 808 is arranged in theapparatus in a vertical direction and the parallel light beam P strikesthe diffraction grating in a perpendicular direction. A beam collector810 in the form of a second diffraction grating is disposed from thefirst diffraction grating 808 and parallel thereto. Behind the beamcollector 810 two decollimation lenses 811 are arranged at equal leveland the light beams leaving these decollimation lenses are eachdeflected and focused onto two CCD cameras 816, through deviation mirrorpairs 812A and 812B, 813A and 813B, and 814A and 814B, and to an opticalimaging system 15.

The beam splitter 808 is supported transversely to the optical axis andfurther comprises a piezoelectric actuating element 817 for shifting thephase of the parallel light beam P by displacing the diffractiongrating.

A holding device 830, for example in the form of a support post, isprovided centrally between the first diffraction grating and the seconddiffraction grating. A wafer or specimen 809 to be measured is held onthe holding device 830 such that both plane surfaces 831 and 832 arearranged in vertical direction parallel to the light beam P. The wafer809 is supported by the support post substantially at its vertical edge833 only so that both surfaces 831 and 832 are not substantiallycontacted by the support post and are freely accessible to theinterferometric measurement.

Moreover, a receiving device (830, 825) may be provided for the wafer809 to be measured. The wafer can be inserted into the receiving devicein a horizontal position. By means of a tilting device 826 the wafer 809may be tilted from its horizontal position into the vertical measuringposition, and the wafer 809 may be transferred, by means of apositionable traveller, into the light path between the firstdiffraction grating and the second diffraction grating so that thesurfaces 809 and 832 to be measured are aligned substantially parallelto the undiffracted light beam P and in a substantially verticaldirection.

Furthermore, a reference apparatus 820 may be provided which comprises areference body 821 having at least one plane surface 824. The referencebody 821 can be introduced into the light path between the firstdiffraction grating 808 and the second diffraction grating 810 in placeof the semiconductor wafer or specimen 809 to be measured by means of atraveller 823 with a linear guide 818. The reference body 821 is held sothat its plane surface 824 is arranged in vertical direction parallel tothe undiffracted light beam P. The reference body 821 can be turned by180° in its mounting around an axis parallel to its surface 824.

In operation the wafer or specimen 809 to be measured is first insertedinto the wafer receiving device 825. The surfaces 831 and 832 arehorizontally arranged. By means of the tilting device and of thetraveller 819 the wafer to be measured is brought into the holdingdevice 830 where it is arranged so that the surfaces 831 and 832 arevertical. A diffraction of the parallel light beam P striking the firstdiffraction grating 808 of the beam splitter produces partial lightbeams A, B, whereby the partial light beam A having a positivediffraction angle strikes the one surface 831 of the wafer 809 and isreflected thereat, whereas the partial light beam B with a negativediffraction angle strikes the other surface 832 of the wafer and isreflected thereat. The 0-th diffraction order of the parallel light beamP passes through the first diffraction grating 808 and is not reflectedat the surfaces 831 and 832 of the wafer 809. This partial light beam Pserves as references beam for interference with the reflected wavefronts of the beams A and B. In the second diffraction grating 810, thebeam collector and the reflected partial light beams A and B are eachcombined again with the reference beam P of the 0-th diffraction orderand focused, in the form of two partial light beams A+P and B+P onto thefocal planes of the CCD cameras 816 through decollimation lenses 811 anddeviation mirrors 812, 813 and 814 as well as positive lenses 815.

During the exposure of the surfaces the phase of the parallel light beamP is repeatedly shifted by 90° and 120° by displacing the diffractiongrating. This produces phase shifted interference patterns. The definedshift of the interference phase produced by the phase shifter 817 isevaluated to determine whether there is a protuberance or a depressionin the measured surfaces 831 and 832 the two digitized phase patternsare subtracted from each other.

A calibration using the reference body 821 can be performed before eachmeasurement of a wafer 809. The reference body 821 is introduced intothe beam path between the first diffraction grating 808 and the seconddiffraction grating 810. The known plane surface 824 is measured.Subsequently the reference body 821 is turned by 180° and the samesurface 824 is measured as a second surface.

FIG. 3 illustrates the measurement model without a wafer or specimenpresent. From FIG. 3, light source 301 initially emits light energy andis focused to strike first mirror surface 302 and second mirror surface303 (not shown). Each of these two mirror surfaces direct light energythrough first collimating lens 112 (not shown in this view) and lightenergy strikes the two surfaces of specimen 111 (also not shown)simultaneously. After striking the two surfaces of specimen 111, lightenergy is directed through second collimating lens 113 (also not shownin FIG. 2) and to third mirror 304 and fourth mirror 305, which directlight energy toward focusing element 306 and detector 307. Imaging arm311 represents the light image path from third mirror 304 towardfocusing element 306. Focusing elements and sensors are those known inthe art, and may include a lensing arrangement, such as multiple lenses,and a CCD or other imaging sensor. Other implementations of focusingelement 306 and detector or sensor 307 are possible while still withinthe scope of the current invention.

From FIG. 1B, the specimen 111 is mounted to three points, includingpoint 201, which are fixedly mounted to mounting surface 116. Mountingsurface 116 may be fixedly mounted to translation surface 117. Eithertranslation surface 117 or mounting surface 116 is fastened totranslation stage 308, which provides translation or sliding of themounting surface 116 and specimen 111 within and into the arrangementshown in FIG. 3. The arrangement may further include translation surface117 depending on the application. Translation stage 308 permits thearrangement of FIG. 1B, specifically wafer or specimen 111, points 201,202, and 203, mounting surface 116, and translation surface 117, to moveup and down in a relatively limited range, as described below. In suchan arrangement employing translation surface 117, the translationsurface and the mounting surface along with the contact points arepositioned within the measurement module 300, preferably by affixing thetranslation surface 117 to the translation stage 308. Specimen 111 isthen physically located between damping bars 114 and 115, as well asproximate damping bar 309 and fastened to points 201, 202, and 203. Oncethe specimen 111 has been adequately fastened to points 201, 202, and203, an inspection of the lower portion of the wafer is initiated. Aftercompleting an adequate inspection, i.e. an inspection of one portion ofthe specimen 111 with acceptable results, the translation stage 308 andultimately the wafer are repositioned or translated such as by drivingthe translating stage 308 along track 310 such that another portion ofthe wafer 111, such as the remaining approximately half of specimen 111is within the imaging path. The other portion of the wafer is thenimaged, and both of the two sided images of the wafer surface are“stitched” together.

The damping bars may have varying size while still within the scope ofthe current invention, as discussed above. In FIG. 3, the damping barsare affixed to end pieces 310 and 311, but any type of mounting willsuffice as long as the gap spacing described above and the ability toperform scans on desired portions of the wafer is available.

As may be appreciated, other means for presenting the remaining portionof wafer or specimen 111 may be employed, such as rotating the wafer byhand by releasing contact with the points and rotating the wafermanually. Alternately, a mechanical rotation of the specimen may occur,such as by rotatably mounting the mounting surface 116 on thetranslating surface 117 while providing for two locking positions forthe mounting surface 116. In other words, the arrangement of wafer 111,points 201, 202, and 203, and mounting surface 116 would initiallyfixedly engage translation surface 117. On completion of a firstinspection scan of a portion of specimen 111, wafer 111, points 201,202, and 203, and mounting surface 116 would be unlocked fromtranslation surface 117 and be mechanically or manually rotatedvertically on an axis perpendicular to translation surface 117. Thewafer and associated hardware rotate 180 degrees to a second lockingposition, wherein the surface would lock and a second inspection scanwould commence. During this rotation scheme, damping bars andimpediments would be mechanically or manually removed to prevent contactwith mounting points 201, 202, and 203. The various components,particularly mounting surface 116, are sized to accommodate rotationwithin the measurement module 300 without contacting the translationstage or other module components.

Alternately, scanning may be performed using multiple two-sidedinspections of the module, such as three, four, or five scans ofapproximate thirds, quarters, or fifths of the specimen. While multiplescans require additional time and thus suffer from increased throughput,such an implementation could provide for use of smaller optics, therebysaving on system costs. Numerous sub-aperture scans may be performed bya system similar to that illustrated in FIG. 3 while still within thescope of the current invention.

FIGS. 4A and 4B illustrate a rotational scanning arrangement of thewafer or specimen 111. As may be appreciated, in a two phase scan of adual sided specimen, at least 50 percent of the surface must be scannedin each phase of the scan. It is actually preferred to scan more than 50percent, such as 55 percent, in each scan to provide for a comparisonbetween scans and the ability to “stitch” the two scans together. Insuch an arrangement, as shown in FIG. 4A, over 50 percent of the surfaceis scanned initially, shown as portion A of the surface 111. Portion Bis obscured by one of the damping bars. After the initial scan phase,the specimen 111 is rotated manually or mechanically to the positionillustrated in FIG. 4B. Approximately 55 percent of the wafer surface,both front and back, are scanned during this second phase. This providesan overlap of five percent of the wafer, and comparisons between theseoverlap portions provides a reference for stitching the scans together.In FIG. 4B, the A portion of the wafer is obscured by the damping bar.

Alternately, as in the arrangement shown in FIG. 3, the wafer orspecimen 111 may be translated vertically and two or more separate scansperformed. As shown in FIGS. 5A and 5B, a portion of the wafer 111 ispositioned between two damping bars, such as damping bars 114 and 115,and the portion marked “B” in FIG. 5A is scanned. As shown therein,greater than 50 percent of the specimen 111 is scanned so that theoverlapping portion may be stitched with the second scan. After theinitial scan, the wafer is translated to a position as shown in FIG. 5B.Portion “A” of FIG. 5B is then scanned, while the lower damping barcovers much of section “B.” The overlapping portions of the two scansare then stitched together to provide a full representation of thesurface, and again such a scan is dual-sided. least 50 percent of thesurface must be scanned in each phase of the scan. It is actuallypreferred to scan more than 50 percent, such as 55 percent, in each scanto provide for a comparison between scans and the ability to “stitch”the two scans together. In such an arrangement, as shown in FIG. 4A,over 50 percent of the surface is scanned initially, shown as portion Aof the surface 111. Portion B is obscured by one of the damping bars.After the initial scan phase, the specimen 111 is rotated manually ormechanically to the position illustrated in FIG. 4B. Approximately 55percent of the wafer surface, both front and back, are scanned duringthis second phase. This provides an overlap of five percent of thewafer, and comparisons between these overlap portions provides areference for stitching the scans together. In FIG. 4B, the A portion ofthe wafer is obscured by the damping bar.

Alternately, as in the arrangement shown in FIG. 3, the wafer orspecimen 111 may be translated vertically and two or more separate scansperformed. As shown in FIGS. 5A and 5B, a portion of the wafer 111 ispositioned between two damping bars, such as damping bars 114 and 115,and the portion marked “B” in FIG. 5A is scanned. As shown therein,greater than 50 percent of the specimen 111 is scanned so that theoverlapping portion may be stitched with the second scan. After theinitial scan, the wafer is translated to a position as shown in FIG. 5B.Portion “A” of FIG. 5B is then scanned, while the lower damping barcovers much of section “B.” The overlapping portions of the two scansare then stitched together to provide a full representation of thesurface, and again such a scan is dual-sided.

From FIGS. 4A, 4B, 5A, and 5B, it should be apparent that a singledamping bar is required if the specimen 111 is to be rotated as shown inFIGS. 4A and 4B, while two damping bars are required if the wafer 111 isto be translated, as shown in FIGS. 5A and 5B. Note that due tomeasurement setup, an arbitrary piston or DC offset and tilt will beapplied to each of the measurements, indicating that some correction isrequired prior to or during stitching to obtain an accurate surfacerepresentation.

FIG. 6 illustrates a general scanning and stitching algorithm for use inaccordance with the invention described herein. The algorithm begins instep 601 and performs the first scan in step 602, as well as determiningthe piston and tilt of the specimen 111. The algorithm evaluates whetherthe scan is acceptable in step 603, either performed by an operatoractually evaluating the scan or a mechanical comparison with a known orprevious scan. If the scan is acceptable, the algorithm proceeds to step604 where the wafer is repositioned to the next location. If the scan isnot acceptable, the wafer is rescanned in its original position. Pistonand tilt may be recomputed, but as the wafer has not moved this is notnecessary. Once the wafer has been repositioned in step 604, asubsequent scan is performed in step 605 and the tilt and pistoncomputed for the new orientation. The acceptability of the scan isevaluated in step 606, and if unacceptable, the scan performed again.The piston and tilt again do not need to be recalculated. Once the scanis mechanically or visually deemed acceptable, the algorithm determineswhether the entire surface has been scanned in step 607. If the entiresurface has not been scanned, the wafer is again repositioned and theremaining scans performed in accordance with the illustrated steps. Ifthe entire surface has been scanned, the algorithm sets x equal to oneand y equal to 2 in step 608. In step 609 the system alters scan x fortilt and piston and separately alters scan y for its respective tilt andpiston. At this point scans x and y are neutrally positioned and may bestitched together. Step 610 is an optional step of performing anadditional stitching procedure. Additional stitching procedures include,but are not limited to, curve fitting the points between the overlappingportions of the two scans using a curve fitting process, replacingoverlapping pixels with the average of both data sets, or weighting theaveraging in the overlapping region to remove edge transitions by usinga trapezoidal function, half cosine function, or other similarmathematical function. Background references are preferably subtractedto improve the stitching result. If significant matching between thescans is unnecessary, such as in the case of investigating forrelatively large defects, simply correcting for tilt and piston mayprovide an acceptable result, and step 610 need not be performed.However, in most circumstances, some type of curve fitting or scanmatching is necessary. Scans are matched and stitched in step 611. Suchstitching algorithms should preferably be performed using a computingdevice, such as a microprocessor (not shown).

Step 612 evaluates whether the complete wafer has been stitchedtogether. If it has not, the algorithm proceeds to increment x and y instep 613 and perform additional stitching of the remaining portions. Ifthe complete wafer has been stitched, the algorithm exits in step 614.

Based on the disclosure presented above and in particular in connectionwith that shown in FIG. 3, the wafer 111 is generally repositioned whilethe inspection energy source and optics remain fixed. While thisimplementation provides distinct advantages in setup time for performingmultiple dual-sided wafer scans, it is to be understood that the lightsource and associated optics and detector may be slidably orrotationally mounted while the wafer remains fixed. In the configurationillustrated in FIG. 3, source 301, support elements 310 and 311, dampingbars 114 and 115, damping bar 309, the four mirrors 302, 303, 304, and305, focusing element 306, and detector 307 may be mounted to a singlesurface and fixedly positioned relative to one another, and translatedor rotated about the wafer. Alternately, the components may betranslated either together or individually to perform subsequent scansof the wafer or specimen 111.

While the invention has been described in connection with specificembodiments thereof, it will be understood that the invention is capableof further modifications. This application is intended to cover anyvariations, uses or adaptations of the invention following, in general,the principles of the invention, and including such departures from thepresent disclosure as come within known and customary practice withinthe art to which the invention pertains.

1. A system for inspecting a semiconductor wafer, comprising: means fordirecting light energy toward the semiconductor wafer for saidinspecting; means for damping the semiconductor wafer, said dampingmeans comprising at least one element mounted in relatively closeproximity to said semiconductor wafer, said damping means and saidsemiconductor wafer being spaced apart by a gap free of components; andmeans for receiving the reflected light energy from the semiconductorwafer, wherein said receiving means are employed for said inspecting. 2.The system of claim 1, further comprising: a positioning arrangement tofixedly maintain the semiconductor wafer in a predetermined position;and a repositioning arrangement for repositioning said positioningarrangement relative to the directing means.
 3. The system of claim 2,wherein said receiving means receive light energy from saidsemiconductor wafer and provide a representation thereof, said systemfurther comprising a stitching device to stitch multiple semiconductorwafer representations together.
 4. The system of claim 1, said dampingmeans comprising a damping bar, and said gap being approximately 0.10 to1.0.
 5. The system of claim 2, wherein said repositioning arrangementcomprises translating means for translating said semiconductor wafer. 6.The system of claim 3, wherein said directing means direct light energyto a predetermined portion of said semiconductor wafer unobstructed bythe damping means.
 7. The system of claim 3, wherein the positioningarrangement comprises a three point kinematic mount, wherein all pointsof the three point kinematic mount are substantially tangentiallyoriented.
 8. A method for inspecting both sides of a semiconductorwafer, comprising: directing light energy toward each side of thesemiconductor wafer; damping the semiconductor wafer by mounting asubstantially rigid element proximate the semiconductor wafer, therebyforming a gap between said substantially rigid element and saidsemiconductor wafer free of components; and receiving light energyreflected from the semiconductor wafer.
 9. The method of claim 8,wherein said light energy is directed by an illuminator, the methodfurther comprising: fixedly maintaining the semiconductor wafer in apredetermined position prior to said directing; and repositioning saidpositioning arrangement relative to the illuminator after saidreceiving.
 10. The method of claim 9, wherein said receiving comprisesreceiving light energy from said semiconductor wafer and providing arepresentation thereof, said method further comprises stitching multiplesemiconductor wafer representations together.
 11. The method of claim 8,wherein said substantially rigid element comprises a damping bar, andsaid gap is approximately 0.10 to 1.0 millimeters.
 12. The method ofclaim 9, wherein said repositioning comprises translating saidsemiconductor wafer.
 13. The method of claim 10, wherein said directingcomprises directing light energy to a predetermined portion of saidsemiconductor wafer unobstructed by the substantially rigid element. 14.The method of claim 9, wherein the fixedly maintaining comprises holdingthe semiconductor wafer using a three point kinematic mount, wherein allpoints of the three point kinematic mount are substantially tangentiallyoriented.
 15. A system for inspecting a semiconductor wafer, comprising:a light emitter emitting light energy toward the semiconductor wafer; asubstantially rigid damping member positioned proximate thesemiconductor wafer, thereby forming a gap free of components betweenthe substantially rigid damping member and the semiconductor wafer; anda detector for receiving light energy reflected from the semiconductorwafer, wherein said detector is employed in said inspecting of saidsemiconductor wafer.
 16. The system of claim 15, further comprising: apositioning arrangement to fixedly maintain the semiconductor wafer in apredetermined position; and a repositioning arrangement forrepositioning said positioning arrangement relative to the lightemitter.
 17. The system of claim 16, wherein said detector receiveslight energy from said semiconductor wafer and provide a representationthereof, said system further comprising a stitching device to stitchmultiple semiconductor wafer representations together.
 18. The system ofclaim 15, said substantially rigid damping member comprising a dampingbar, and said gap being approximately 0.10 to 1.0 millimeters.
 19. Thesystem of claim 16, wherein said repositioning arrangement comprisestranslating means for translating said semiconductor wafer.
 20. Thesystem of claim 17, wherein said light emitter directs light energy to apredetermined portion of said semiconductor wafer unobstructed by thesubstantially rigid damping member.
 21. The system of claim 16, whereinthe positioning arrangement comprises a three point kinematic mount,wherein all points of the three point kinematic mount are substantiallytangentially oriented.